The present invention relates generally to semiconductor device manufacturing, and more specifically to deflashing of packaged semiconductor devices.
One method of packaging semiconductor die involves attaching multiple die, or dice, onto leadless leadframe substrate panels that contain arrays of die attach pads. Generally, leadless leadframes include die attach pads that are surrounded by respective sets of electrical contact landings, wherein a die is attached to each of the die attach pads and electrically connected to each of the contact landings within a set. The contact landings provide the physical connection between the input and output terminals of the die and those of a printed circuit board. As with all delicate electronic components, such as integrated circuit chips, molding material is then applied to encapsulate the die and to fix the orientation of the contact landings. See FIG. 1, which illustrates a top plan view of a top surface of a molded leadless leadframe panel 100. The panel 100 includes molding caps 102, which encapsulate the dice that have been placed within each of the leadless leadframe panel. A problem with the process of applying the molding material is that the molding material often coats more than the die and ends up coating part of the contact surfaces of the contact landings and the die attach pads. Such excess resin is referred to herein as xe2x80x9cmold-flashxe2x80x9d or xe2x80x9cflash.xe2x80x9d
FIG. 2 illustrates a top plan view of a bottom surface of the molded panel 100 having exemplary occurrences of flash. In molded panel 100, molding material has seeped through to the bottom surface of the leadless leadframe panel and has formed thin layers of flash 200. Areas of flash 200 are undesirable, as they are physical obstructions that prevent the strong connections required between singulated semiconductor device packages and printed circuit boards. Flash area 200a, which is formed over contact landings 204, is particularly undesirable as it prevents the electrical connection between the contact landings 204 and the printed circuit board. Therefore, mold-flash must be removed from the bottom surface of leadless leadframe packages during the semiconductor device manufacturing process.
Conventional methods for removing mold-flash include high-pressure impact actions, e.g., wet or dry media honing, and reactive chemical actions, e.g., electrolytic deflashing. Unfortunately, however, these methods have been developed to deflash two-sided leadframe based molded packages. Consequently, these methods are not effective for one-sided leadframe based molded packages, like leadless leadframe packages, because they tend to damage the leadless leadframe panel and they are unable to completely remove the flash. A problem specific to high-pressure impact methods relates to the fact that mechanisms for holding the leadless leadframe panels may not be able to securely hold the panels to withstand the high-pressure conditions. As a result, the panels may drop out of position for deflashing and thereby lead to manufacturing yield losses. Additionally, the conventional methods are generally not cost effective because they involve high operating costs and high equipment investment costs. One factor that increases the operating costs is that the equipment for the conventional methods require large production floor space.
In view of the foregoing, a system and a method for removing mold-flash from leadless leadframe packages without damaging the leadless leadframe panel would be desirable.
The present invention is directed to a system for removing mold-flash from leadless leadframe substrate panels without damaging the substrate leadframe panel. The system of the present invention uses a rotary buffing device for removing the mold-flash. The leadless leadframe substrate panels have bottom surfaces that contain electrical contact landing and die attach pad surfaces. Covering at least some of the surfaces of the electrical contact landings and the die attach pads are formations of mold-flash, which are thin layers of molding material. The rotary buffing device is rotated at a sufficiently high rate such that the formations of flash are brushed (or buffed) off the bottom surfaces as the rotary device is run along the substrate panels.
In another aspect of the invention, a method for using the system is described.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example the principles of the invention.